A quick check you can try is rename those two files and replace them with fresh copies from the phpBB download, you can change them back easily if it doesn’t clear the error. What are you using to edit the php files and or what method?

A quick check you can try is rename those two files and replace them with fresh copies from the phpBB download, you can change them back easily if it doesn’t clear the error. What are you using to edit the php files and or what method?

I did just that. Replaced with originals, purged the cache and retried. Same error. Also happens in the ACP when trying to deactivate or delete a custom profile field.
Would it be safe to just upload the original 3.2.1 package and overwrite all files?